Which plant tissue of the root is responsible for the formation of root nodules in plants of the family $Fabaceae$?

In leguminous plants,root nodules are formed by which of the following?

We find that $Rhizobium$ forms nodules on the roots of leguminous plants. Also,$Frankia$,another microbe,forms nitrogen-fixing nodules on the roots of the non-leguminous plant $Alnus$. Is it necessary for a microbe to be in close association with a plant to provide mineral nutrition? Explain with the help of one example.

Select the correct statements from the given:
$(a)$ Nitrogenase is a heterodimeric protein.
$(b)$ Root hairs curl by action of nitrogenase and plant 'nod factors'.
$(c)$ During symbiotic $N_2$ fixation,$ATP$ is provided by the legume plant.

What will happen if $Rhizobium$ bacteria are introduced into a wheat field?

Which of the following is a symbiotic nitrogen fixer?